1. Field of the Invention
The present invention relates to optical lenses, and more particularly, to a piezoelectrically driven optical lens.
2. Description of the Prior Art
British 1 Ltd. Corporation (http://www.1limited.com) has developed a piezoelectric actuator that is helical and curled and made of twin-chip piezoelectric ceramic plates, which, when coupled with an optical lens and a bracket and incorporated into a film camera, digital camera, or camera phone, provides for automatic focus alignment.
Despite its advantages, namely small size, great actuation displacement, low energy consumption, low noise, and high compatibility, the helical, curled piezoelectric actuator does have its own drawbacks. Coiling up twin-chip piezoelectric ceramic plates to form a helical, curled piezoelectric actuator and linking up circuits entail much labor; even if the process is performed with automated machines and tools, the process is complicated and sophisticated, and, therefore, both yield and quality of product will typically be unreliable. Hence, incorporation of the helical, curled piezoelectric actuator in a film camera, digital camera, or camera phone has little industrial applicability because of high manufacturing costs and low yield.
U.S. Pat. Nos. 4,755,705, 4,786,836, 4,829,209, 4,935,659, 4,952,834, 4,959,580, and 5,013,982 disclose technology related to an ultrasonic motor (also known as piezoelectric motor). U.S. Pat. Nos. 5,708,872, 5,751,502, 5,898,526, and 5,898,528 disclose the technology for incorporating an ultrasonic motor (also known as piezoelectric motor) into a conventional camera. Due to the relatively large volume occupied by conventional cameras, it is feasible to fabricate or drive an optical lens, using a known device or technology, such as the aforesaid ultrasonic motor (also known as piezoelectric motor) or the technology thereof. Nonetheless, with digital cameras increasingly replacing conventional cameras, and with camera phone lenses with zooming and focusing functions becoming popular and typical of cellular phones, the aforesaid conventional ultrasonic motor (also known as piezoelectric motor) is too large to be placed inside a digital camera or camera phone. This is the primary reason why the optical lenses of digital cameras and that of camera phones on the market remain relatively large.
U.S. Pat. No. 6,710,950 discloses a piezoelectric actuator for use in digital cameras. The piezoelectric actuator comprises a plurality of piezoelectric elements positioned symmetrically on an outer surface of a fixed support tube and an inner surface of a circuit board. An engagement pad is disposed on the surface of each of the piezoelectric elements. Once the piezoelectric elements are subjected to an applied voltage, the engagement pads synchronize the movement of the lens in the axial direction of the fixed support tube, thereby adjusting the position of the lens. But the technique involves using a plurality of piezoelectric elements and thereby results in high costs and a complicated assembly process, not to mention that it is difficult to achieve precise control of displacement in the course of synchronized movement of the lens.
U.S. Pat. No. 6,853,507 discloses a lens driving device for use in an optical device to move the lens quickly and provide focus adjustment within an effective distance. Unlike U.S. Pat. Nos. 6,710,950, 6,853,507 discloses driving a lens system to move axially inside a lens barrel by means of a helical groove (whereby rotational movement is transformed into axial movement), and U.S. Pat. No. 6,853,507 also discloses a ring-shaped piezoelectric actuation element disposed in the bottom and adapted to enable rotational movement of the lens barrel. In response to an applied voltage, the ring-shaped piezoelectric actuation element is radially contracted or expanded to drive the lens barrel to perform optical focus adjustment or focus alignment. Nevertheless, this patent involves fabricating a plurality of piezoelectric actuation elements each having an inner circumferential surface disposed with a plurality of segments, and thus precise control of the fabrication process is difficult, not to mention that two-way rotational movement cannot be achieved without two ring-shaped piezoelectric actuation elements and two helical grooves oriented in different directions, which accounts for the disadvantages of this patent, such as high costs and a complicated assembly process. Besides, the ring-shaped piezoelectric actuation elements work by means of a surface wave and thereby works inefficiently, and thus the ring-shaped piezoelectric actuation elements disadvantageously slow down rather than speed up an optical device.
In addition to the aforesaid patents, digital cameras and camera phones with small-sized piezoelectrically driven optical lens are disclosed in some papers and at some conferences. However, parts and components of a conventional piezoelectrically driven optical lens have complex structures that require sophisticated processing and therefore are fabricated by unit production instead of batch production. In addition to the fabrication process, the intricate parts and components of the conventional piezoelectrically driven optical lens make the assembly process difficult, which is particularly true when it comes to a piezoelectric stator. Assembling the piezoelectric stator is difficult, and the designs employed typically reduce the driving force of a simple piezoelectrically driven optical lens. Small-sized elements cannot be easily fabricated with an automated machine, leading to increased labor costs and higher manufacturing costs being incurred in their fabrication. In short, despite its advantageous small size, a conventional piezoelectrically driven optical lens does not offer much in the way of cost-competitiveness, commercial value, or industrial applicability.
In view of the aforesaid drawbacks of the prior art, an issue calling for urgent solution is to develop a piezoelectrically driven optical lens characterized by structural simplicity, high torque, small size, strong structure, ease of production, and ease of assembly.